Ray McDonald’s father was a receiver for the Florida Gators. His grandfather was a running back for Bethune-Cookman.

So how did Ray end up on the defensive side?

“I probably got my size from my mom’s side of the family,” he said with a laugh.

The 49ers are happy McDonald inherited the D-line chromosome. The 6-foot-3, 290-pounder has sacks in each of the first two exhibition games, raising hopes that the team’s long-lost pass rush will finally reemerge.

The 49ers managed just 31 sacks last season; only Atlanta (25) and Carolina (23) were worse among NFC teams.

Against the Green Bay Packers on Saturday, however, the 49ers registered six sacks — including 11/2 by McDonald.

“I’m more focused this year. I know what I have to do,” he said Monday. “Coming in as a rookie, I didn’t really know what to expect. Learning a new defense, having to play a new technique — it was all new to me.”

A third-round draft pick from Florida in 2007, McDonald made a minimal contribution (11 tackles, one sack). But he came back stronger and about 10 pounds heavier this season, giving him some strength to go along with the speed he inherited from his father’s side.

McDonald demonstrated his power against the Packers, using a bull rush to embarrass 300-pound guard Jason Spitz.

“When you can beat an offensive lineman like that, you feel great,” McDonald said. “And to get a sack at the end of it is an even bigger plus.”

The Packers were seeing what the 49ers’ offensive linemen see every day in practice. Guard Adam Snyder said McDonald has figured out “what he does best” in terms of using his strength and long arms to create havoc.

Tackle Joe Staley put it in more basic terms.

“Ray McDonald,” he said, “is 20 times better than he was last year.”

Right tackle Jonas Jennings will be sidelined for the game in Chicago on Thursday because of a broken knuckle on his right hand. Jennings underwent surgery Monday but is expected to return for the exhibition finale against San Diego on Aug. 29.

Jennings will wear a protective device on his hand for an undetermined about of time, but Coach Mike Nolan is hopeful that the equipment will not be restrictive.

It is the latest injury for Jennings, who has missed all or parts of games 32 times in 48 regular-season games since signing with the 49ers in 2005.

Three receivers will also miss the game Thursday: Arnaz Battle (hamstring), Bryant Johnson (hamstring) and Ashley Lelie (calf). The others declared out are guard David Baas (pectoral), running back Michael Robinson (knee) and safety Lewis Baker (thigh).

Cornerback Tarell Brown (hip) returned to practice on a limited basis.

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